1. Technical Field
The present invention relates mainly to a combined spectacle lens having a progressive power for a person having presbyopia eyes with low amplitude of accomodation and an auxiliary lens used for the combined spectacle lens, and a method of edging the lenses.
2. Related Art
A progressive-power lens is used mainly as a vision corrective lens for a person having presbyopia eyes with low amplitude of accomodation, and is a lens in which a power is changed continuously from a power required for viewing an object at a distance or an intermediate distance to a power required for viewing an object nearby on one piece of lens without no boundary so that it has a fashionable looking.
Optical performance of the progressive-power lens basically depend on a progressive corridor length which corresponds to a distance on a principal meridian of a progressive portion in which the power is continuously changed and an addition power which is a difference of the power of the progressive portion. As one of designs according to applications, for example, there is so-called a distance-near type, which is designed in such a manner that both of a distance visual field and a near visual field are arranged in well-balanced manner and the progressive corridor length is set to a value on the order of 10 to 16 mm so as to allow a user to rotate the eye easily when viewing an object nearby. There are also so-called an intermediate-near type which is intended mainly to be used for viewing an intermediate area of about 1 meter to an area nearby, and a near-near type which is intended specifically to be used for viewing an object nearby. The intermediate-near type and the near-near type are designed to have the long progressive corridor length on the order of 19 to 25 mm in order to realize a wide visual field in an intermediate view. In this manner, the optimal optical performance for different applications cannot be obtained in one design.
When going out, a comfortable visual field can be obtained by using the distance-near type which is intended mainly to be used for a distance view. During deskwork or when working in a room, a comfortable visual field can be obtained by using the intermediate-near type or the near-near type. In order to obtain a comfortable visual field both when going out and working in a room, it is necessary to prepare the distance-near type lenses and the intermediate-near type lenses in respective spectacle glass frames respectively.
However, in this circumstance, it is necessary to purchase lenses of different designs, and also to purchase the spectacle glass frames for each type of lenses, and hence the cost is increased. Therefore, it will be very convenient if the design type of the progressive-power lens can be changed easily by combining the spectacle lenses.
A technique to combine two spectacle lenses is publicly known and, as shown in JP-A-2003-315751 and Japanese Utility Model Registration No. 3030336, spectacle glasses of a front-hanging type, which are configured in such a manner that a sub-lens can be detachably attached to a front surface of a normal spectacle lens as a basic lens with a clip mechanism or the like, are known.
In Japanese Patent No. 2519921, a technique in which two progressive-power lenses are used for counterbalancing or alleviating progressive change of the power in one lens for improving aberration and hence improving the visual field is proposed. However, it simply provides a monofocal view, and is not designed to be optimal for different applications.